Firstly, the one acre can only be transferred tax free to your wife, if it is transferred into your joint names CGT will apply to your MIL's deemed gain.
On the CGT on the remaining acre, there isn't really any way to get around it. I take it you are going to pay the CGT on it. You won't be doing too bad, getting land worth €60k in total for just €6k.
Has your MIL been farming this land? If so, perhaps retirement relief could be claimed and thereby eliminate the CGT.
Should you sell this land in the future your deemed base cost will be €30k an acre.